Process for the Synchronization of Ovulation for Timed Breeding Without Heat Detection

ABSTRACT

A method for synchronizing ovulation in sows and gilts by a single injection of hormones is disclosed. A hormone, gonadotropin releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG), analogues, derivatives, agonists or combinations thereof is administered to an open sow post weaning at a specific time to stimulate ovulation of mature responsive follicles. The sow is then bred, without heat detection, at a specific subsequent timed interval after injection with hormone, with one or two artificial or natural breedings. In gilts, the hormone is injected at a timed interval from onset of estrus or at a specific timed interval following Prostaglandin F2 a  for those gilts which have been held in a state of pseudopregnancy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Ser. No. 60/508,509 filed Oct.3, 2003 entitled “Process for the Synchronization of Ovulation for TimedBreeding Without Heat Detection” by James W. Lauderdale.

FIELD OF THE INVENTION

This invention relates to the reproductive management of sows and giltsand more particularly processes for synchronizing ovulation in suchswine for timed artificial breeding with a reduction in or with noregard to estrus detection.

BACKGROUND OF THE INVENTION

The administration of hormones to control the reproductive process indomestic animals such as horse, cows, sheep, goats and swine is wellknown in the art. One approach to managing reproductive processes indomestic mammals involves the direct administration of gonadotropins todomestic animals. Gonadotropins are produced by the anterior lobe of thepituitary gland and are characterized as follicle stimulating hormone(FSH) and luteinizing hormone (LH). Typically such hormones areextracted from the porcine pituitary glands and are administered todomestic animals to control or stimulate the ovulatory process. Onegonadotropin formulation is FSH-P produced by Schering-Plough Corp.FSH-P has a fairly high and variable content of luteinizing hormone andwhile effective in producing an ovulatory response, has been less thandesirable in producing high fertilization rates and viable embryos.Another formulation, which contains a low and controlled level ofluteinizing hormone with high follicle stimulating activity, isdisclosed in U.S. Pat. No. 4,780,451to Donaldson. Gonadotropin releasehormone (GnRH) can also be used to stimulate ovulation as related inU.S. Pat. No. 5,180,711 to Hodgen. In that instance GnRH is administeredsubsequent to a GnRH antagonist which effectively suppressed naturalgonadotrapin levels. The GnRH then stimulates the release of endogenousFSH and LH leading to follicle development and ovulation. The use ofsimilar hormones for control of ovulation in cattle is described in U.S.Pat. No. 5,589,457 to Wiltbank.

A number of different preparations of gonadotropins are availablecommercially including Fertagyl, Cystorelin, ChoruIon, Folltropin-V,Factrel, PG600, Receptal and others. In addition, certain GnRH analogs,or agonists, such as deslorelin and buserelin are also available. Thesehormones may be administered to the various domestic species by implant,by intramuscular or subcutaneous injection or by mucosal applicationssuch as intranasal and intravaginal routes. Gonadotropins may also beadministered with excipients or delivery systems, which delay or controlthe release over time to produce more natural or even extended releasepatterns of LH. See U.S. Pat. No. 6,051,558 to Burns, et. al.

A major goal of commercial swine production is to maximize reproductiveefficiency. Increased reproductive efficiency offers producerssubstantial opportunities to reduce production costs and enhanceprofitability. Part of the production costs is the result of a heavyreliance on daily heat detection of individual animals (W. L. Flowersand H. D. Alhusen, (1992) J. Animal Science 70:615-621) since gilts andsows are bred based on spontaneous estrus cycles. Approximately half ofthe labor in swine breeding facilities is devoted to detection of estrusin breeding gilts and sows. Gilts or sows must be checked at least oncedaily in order to be bred at the correct time, and, if artificialinsemination (“AI”) is used, it may be necessary to check twice daily inorder to achieve the best results. Rigorous heat detection is necessarybecause it is difficult to predict the day of heat for any cyclic giltor open sow, even with good heat detection records.

It is therefore an object of the present invention to provide a means ofinducing ovulation that allows for artificial insemination in theabsence of heat detection.

SUMMARY OF THE INVENTION

A method for synchronizing ovulation in swine in order to provide foreffective reproductive management through timed artificial inseminationwithout estrus (heat) detection has been developed. A hormone,gonadotropin releasing hormone (GnRH), luteinizing hormone (LH),follicle stimulating hormone (FSH), human chorionic gonadotropin (hCG)or a combination drug with similar activity such as PG600, isadministered to a postpartum sow at a timed interval post weaning inorder to stimulate ovulation. After a suitable period of time (accordingto breed of swine and farrowing records), a single timed AI breeding isadministered to achieve normal pregnancy rates and litter sizes with noregard to estrus detection.

Preferably the GnRH is administered in the form of 50 mcg of deslorelinin an extended release carrier such as the SAIB excipient available fromBirmingham Polymers. Other GnRH preparations may be administered in therange of 10400 mcg. Such products as hCG may be administered in doses ashigh as 750 IU. The dose amounts as designated herein are for thehormones in their “native form” or in the case of GnRH analogs, such asdeslorelin, are designated as the equivalent amount of the hormone inquestion in the “native form.”

Examples demonstrate that the method of synchronization was highlyeffective as compared to controls requiring much more labor intensivebreeding techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are graphs showing that a single injection of 50 mcgof deslorelin in SAIB produced a LH peak about twice normal value (FIG.1 a), compared to Hansel et al., (1973) Biology of Reproduction 8, 222)(FIG. 1 b), which, returned to base level by 18 hours as determined byRIA.

DETAILED DESCRIPTION OF THE INVENTION

Effective reproductive management of swine has become an importantfactor for swine producers, particularly in view of continued verticalintegration of the industry where the predominant model is an“all-in-all-out” method of production. In this method waves of pigs areproduced for cost efficiencies, disease control and feed rationing toproduce groups of pigs meeting ideal marketing weights at the same time.Reproductive control is the first step in the process whereby farrowinghouses are filled with gilts and/or sows which ate bred to farrow duringa tight interval, usually 5 to 7 days. This assures that weaning ofpiglets from the whole farrowing house can occur on the same day and inturn groups of pigs from any one unit are of the same age, close in sizeand stage of development. In commercial swine husbandry this helpscontrol disease, reduces stress among aggregated groups and maximizesthe utilization of various feed formulations as the pigs proceed towardmarket weight.

It is well known by those skilled in the art of swine production that tomaximize reproductive efficiency estrus detection becomes an importantand major task Estrus is the period of boar or breeding receptivity.Estrus detection, as presently practiced on commercial swine farms, is adaily or twice daily labor-intensive process. The process involvesindividual exposure of each gilt or sow to a boar and manually puttingback-pressure (the “riding test”) on each animal to determine if thestanding heat “immobilization” reflex is triggered (Gordon, I.,Controlled Reproduction in Pigs, CAB International, 1997). This isperformed on each individual in the breeding pool not known to have beenrecently bred and gone out of estrus. The process continues rightthrough the estrus period and the sow or gilt is bred multiple timesuntil it no longer is deemed receptive.

At the start of a normal estrus (heat) in domestic animals, the brainsecretes large amounts of GnRH that in turn causes a release of folliclestimulating hormone and luteinizing hormone (LH) which will causeovulation of the Graafian follicles over a 24-48 hour time period. Inswine, peak estradiol levels occur several days prior to the signs ofestrus and, indeed, the LH peak often occurs at the time estrus isevidenced (Niswender et al Endocrinology 37, 576-580 (1970)).

The duration of the estrus cycle in the sow is relatively constant yearround at 21 days without obvious seasonality (Asdell, (1964) Patterns ofMammalian Reproduction, 2nd edn. Cornell University Press, Ithaca, USA,pp. 670; Dziuk, (199.1) Reproduction in the pig. In: Cupps, P. T. (ed.)Reproduction in Domestic Animals, 4th edn. Academic Press, New York, pp,471-489) although there may be some tendency for less consistency inlate summer (Stork, M. G. (1979) Veterinary Record 104, 49-52; Hurtgenand Leman, (1980) J. Amer. Vet. Med. Ass. 177, 631-635) possibly due toshortened day length. Gilts may tend toward shorter cycles than maturesows (Asdell, (1964) Patterns of Mammalian Reproduction, 2nd edn.Cornell University Press, Ithaca, USA, 670 pp.). Behavioral estrusoccurs over a 2-3 day period, the onset of which is preceded by peakestradiol levels and coincides with peak LH levels (Hansel et al.,(1973) Biol. Repro. 8, 222) which are responsible for the maturation andovulation of follicles (Hunter and Polge, (1966) J. Repro. Fert. 12,525-531; Hunter (1977) Brit, Vet. J. 133, 499-501). Ovulation occursabout 40 hours after the onset of estrus if estrus is 2 days in durationor about 75% of the way through the estrus if it is longer than 2 days(Gordon, 1997 Controlled Reproduction in Pigs, CAB International, 1997).The multiple ovulations occur over approximately 1-6 hours (Betteridgeand Raeside, (1962) Res, Vet, Sci. 3, 390-398; Du Mesnil du Buisson andSignoret, 1970 Du Mesnil du Boisson, F. and Signoret, J. P. (1970) Vet.Rec. 87, 562-568; Soede and Kemp, 1993 Soede, N. M. and Kemp, B. (1993)Theriogenology 39, 1043-1053).

Attempted hormonal control of the estrus period and ovulation is welldescribed in the literature. The controls have been described using morethan one steroid/gonadotropin/prostaglandin or their analogs in seriesor combination of injections at various timings depending on the natureof the particular group, including pre-pubertal and pubertal gilts, sowsfarrowed but pre-weaning, at the time of weaning or post weaning.Injectable and oral progesterone and progestagens (Ulberg et al (1951)J. Animal Sci. 10, 665-671); Gerrits et al., (1963) J. Animal Sci. 21,1022-1025), altrenogest (Martinat-Botte et al., 1985 Martinatt-Botte,F., Bariteau, F., Badouard, B. and Terqui, M. (1985) J. Reprod. Fert.Suppl. 33, 211-228) altrenogest with PMSG and GnRH/hCG (Busch et al.,(1992) Monatshefte fur Veteriarmedizin 47, 307-316), prostaglandins(Jackson and Hutchinson, Veterinary Record 106 33-34), methallibure,PMSG and hCG (Paige et al., (1968) Veterinary Record 83, 136-142; F. DeRensis et al., (2003) Animal Reproduction Science 76: 245-250) haveeither met with limited success (progestagens), failed (prostaglandins),been banned from the market (methallibure) or require daily oral dosing(altrenogest), multiple injections (estradiol, progesterone) orcombinations of drugs (PMSG, hCG GnRH) coupled with continued heatdetection in order to create detectable breeding efficiencies.

Those skilled in the art continue to use multiple sequential hormonalintervention in order to control the time of estrus and time ofovulation in the estrous cycling gilt, such as a sequence of altrenogestor methallibure to inhibit pituitary gonadotropin followed by eCG or hCGor a GnRH, and postpartum sow, such as eCG post-weaning followed by aGnRH or a combination of a GnRH and hCG with breeding by a timed AI(Brussow et al, (1996) Theriogenology 46: 925-934). GnRH has beeninvestigated as a “fertility enhancer” in the sow by injecting 1 day or11 to 12 days following first service (Peters et al, (2000) Vet. Record147:649-652). As recently as 2003 (DeRensis et al, 2003), those skilledin the art continued to investigate PG 600 injected at or prior toweaning as a method to shorten the wean to estrus interval but not fortimed ovulation for time breeding. Recent reviews of the hormonalmethods to control estrus and breeding of estrous cyclic gilts andpostpartum sows continue to cite processes as identified above(Kirkwood, (1999) Swine Health Prod. 7(1):29-35; Day, et al. Control ofreproduction in the female pig. 30^(th) Annual Meeting, AmericanAssociation of Swine Practitioners, Workshop #6, St. Louis, Mo. Feb. 27,1999, pp. 23-39). The scientific literature from the early 1960s through2003 reports the requirement for either multiple sequential hormonaltreatments in estrous cycling gilts or the use of various combinationsof or single use of gonadotropins for attempting to manage the time ofestrus in postpartum sows. No one skilled in the art has reported on asingle injection of a GnRH postpartum followed by one or two timedbreedings resulting in normal fertility in the absence of estrusdetection and breeding associated with the detected estrus.

The ultimate goal of synchronizing estrus and/or ovulation, reducingpost weaning to estrus intervals or breeding gilts as replacements is tokeep the farrowing houses full and grouped for all-in-all-outproduction. Meanwhile, all breeding management programs utilize standardheat detection methods throughout the early detection and estrus perioduntil breeding is complete and the gilt or sow is no longer receptive.

There is a wealth of information indicating that hormonal Induction ofestrus post weaning with individual gonadotropins or with a combinationdrug such as PG600 is efficacious in producing a fertile estrus afterweaning (Kirkwood, R. N. (1999) Swine Health Prod. 7(1):29.35; Sechin etal., (1999) Theriogenology 51:1175-1182). However, F. De Rensis et al.state that while injection of gonadotropins at weaning will produce anearlier fertile estrus, by inducing an earlier estrus the time betweenonset of estrus and ovulation increases, making prediction of ovulationeven more difficult (Knox et al. (2001) J. Animal Sci. 79:796-802).Furthermore, the research has demonstrated that the success of inducinga fertile estrus is correlated with the day of lactation when treated,with the highest success correlated to treatment on day 25 post partum(Hodson et al. 1981), which is inconsistent with those commercialprograms which wean 17-21 days after farrowing. In all cases, thesuccess of these experimental protocols was coupled with daily or twicedaily estrus detection through the period of receptivity and withmultiple breedings.

Methods for Administration

The method for synchronizing ovulation in swine without heat detectionincludes the steps of administering to a swine, usually at 21 daysfollowing the time of weaning, a dose of a hormone such as agonadotropin releasing hormone (GnRH), a luteinizing hormone (LH), ahuman chorionic gonadotropin (hCG), derivatives or analogues thereof, orcombinations thereof, in an amount effective to stimulate ovarianfollicle ovulation; and after approximately one day, breeding the sowwithout heat detection. Breeding may be natural or artificial.

Preferably, the swine is a postpartum sow and most preferably thehormone is administered to the sow 96 hours after weaning her piglets.In another embodiment, the swine is a postpartum sow on the first day ofestrus postweaning; and hormone is administered and the swine bredwithout further heat detection. Alternatively, the hormone isadministered at the first detectable signs of estrus.

Preferably, the sow is bred about 28 hours after the hormone isadministered. A second breeding may be performed.

Pubertal gilts may have hormone administered on the first day of estrus,and be bred without further heat detection. In a preferred embodiment,the hormone is administered at the first detectable sign of estrus. Instill another embodiment, the gilt is in a state of pseudopregnancy andhas been administered a dose of Prostaglandin F2a. In one embodiment,the GnRH hormone is administered 48 hours after Prostaglandin F2aadministration, In one embodiment, the swine was pregnant and theProstaglandin F2a was administered for the purpose of synchronizedabortion. In this embodiment, the GnRH is preferably administered 48hours after abortion is completed.

Studies have now demonstrated that a timed injection of a single hormonesuch as deslorelin (GnRH analog) in SAIB excipient and timed breedingwith no heat detection results in normal fertility and piglet numbers inpost weaned sows. The timed injection and timed breeding abruptlycurtails heat detection after the first sign of estrus is detected. Atimed injection of a single hormone, deslorelin (GnRH analog), in SAIBexcipient and timed breeding with no heat detection can also be usedfollowing prostaglandin PGF2a administration in gilts in a state ofpseudopregnancy.

II. Compositions for Synchronization of Estrus

Hormones

The composition contains gonadotropin releasing hormone (GnRH),luteinizing hormone (LH), human chorionic gonadatropin (hCG),derivatives or analogues thereof, and combinations thereof, in an amounteffective to stimulate ovarian follicle ovulation; As demonstrated inthe examples, deslorelin was used at a dose of 50 mcg in SAIBadministered subcutaneously near the vulva. The dosages of comparablehormones in their native form or other GnRH analogs thereof haveapproval for some applications in meat and dairy animals. Subject to therequirements for FDA approval, and, as will be recognized by thoseskilled in the art, such doses may vary since there is currently no FDAapproved swine label indication.

By the term “native form” is meant the hormone having the same aminoacid sequence and the same activity scale as found in nature. Thus, thenative form of GnRH will include the form of the hormone, regardless ofhow synthesized, which is as it is produced by the hypothalamus. GnRHswhich are commercially available under the trademarks Cystorelin orFactrel, are synthetic products of the same amino acid sequences andactivities as naturally occurring in the animal, and are thereforeconsidered to be the native form of the hormone. The dosage rates thatare given herein are for the analog of GnRH, deslorelin, andcorresponding adjustments should be made for the native forms, whichhave lower activity. Thus the dosage of 50 mcg of deslorelin is the doserate for an analog of the GnRH hormone so that a native form having, asone example, one-fifth the activity would have to be dosed at a rate of250 mcg.

Excipients

In the preferred embodiment, the hormone is suspended or dissolved in aninjectable excipient. In the most preferred embodiment, this is amaterial such as SAIB, which is obtained from Durect under the trademarkSABER Tm Delivery System. This uses a high-viscosity base component,such as sucrose acetate isobutyrate (SAIB), to provide controlledrelease of active ingredients. After administration of a SABER™formulation, the solvent diffuses away, leaving a viscous, adhesivematrix of the three components—SAIB, drug, and any additives. Thissystem includes a water insoluble, high-viscosity base component, asmall amount of pharmaceutically acceptable organic solvent, such asethanol, NMP, or Miglyol® 810, to create a low viscosity solution beforeapplication, can be administered via injection, orally, or as anaerosol, and forms an adhesive, biodegradable depot for drug delivery.These can be designed to release drug over a period of one day to threemonths. The more rapid delivery is desired for this application.

Other suitable excipients can also be used. BASF markets PLURONIC™ typematerials, which are block copolymers based on ethylene oxide andpropylene oxide. They can function as antifoaming agents, wettingagents, dispersants, thickeners, and emulsifiers. Other materialsinclude hydrogel forming materials such as collagen, hyaluronic acid,alginate, and fibrin. Many other extended release materials and devicesare also available, including various medical depo devices havingsimilar release profiles. Other extended or sustained releaseformulations can be made using materials such as ion exchange resins orpolymeric delivery devices.

The present invention will be further understood by reference to thefollowing non-limiting examples.

Example 1: Treatment with a Single Dose of Hormone Yielded Higher LitterSizes

A dose response study was performed using deslorelin in SAIB in anovariectomized estrogen primed gilt model (Barb, et at (1999) Proceed.Int'l. Symp. Control. Rel. Bioact. Mater., 26). As shown in FIG. 1 a, 50mcg of deslorelin in SAIB produced a LH peak about twice normal value,compared to Hansel et al., (1973) Biology of Reproduction 8, 222) FIG. 1b, which returned to base level by 18 hours as determined by RIA.

Example 2: Comparison of Intravulvular Administration with Injection ofDesiorelin

Based on these results a study was performed utilizing mature postpartumsows with 75 test individuals and 75 controls. Sows were assignedrandomly in blocks of two to either control or to be injectedintravulvar with 50 mcg of deslorelin in SAIB at the time of estrusdetection for sows first detected in estrus in the a.m. and 12 hourslater for those first detected in estrus in the p.m. Treated animalswere bred AI upon detected estrus and again 24 hours later if still inestrus. Controls received a saline injection on first detected estrusbehavior estrus detection and were bred according to the farm's normalprocedures.

As shown in Table 1, there was no significant difference in pregnancyrates for sows of the Control versus Treated groups but there were 0.6greater number of live piglets born per litter in the treated groupversus control group.

TABLE 1 Estrus and Pregnancy Rates After Deslorelin Treatment In SowsSaline Deslorelin (Control) (Treated) Length of Estrus (Hrs.) 40.74 (n =73) 40.81 (n = 69) Pregnancy Rate 92% (n = 75) 91% (n = 75) Saline sowsbred at detected estrus consistent with farm sows. Deslorelin sowsinjected intravulvar with 1 ml (50 μg deslorelin acetate) at firstestrus detection and AI, then AI again if in estrus the next day. Livepiglet number 0.6> in Deslorelin versus Saline sows.

Example 3: Normal Pregnancy Rates were Attained Following HormoneTreatment in Sows

Approximately 170 postpartum sows were randomly divided into two equalgroups comprised of controls and treated. Following weaning, thecontrols were detected for estrus and bred following the normal standardoperating procedures for the farms on which they resided. The treatedsows received a 50 mcg dose of deslorelin in SAIB at 96 hourspost-weaning and were bred with a single insemination 28+/−2 hours laterwith no regard to estrus detection. The sows were examined for pregnancyby ultrasound at 21 days and slaughtered around 28 days post breeding,The entire reproductive tract was removed and corpora lutea and embryoswere counted.

The data in Table 2 demonstrates that normal pregnancy rates wereattained following a single timed injection of deslorelin in SAIB, at atimed interval post-weaning, followed by a single timed insemination, inthe absence of an estrus (heat) detection.

TABLE 2 Pregnancy Rates and Embryo Numbers After Deslorelin Treatment inSows Preg- Number Sows Live Embryo nancy In Group Pregnant Embryos CLSurvival Rate Controls 82 54 13.6 20.2 68% 66% Treated 84 60 13.4 20.964% 71%

Example 4: Normal Litter Sizes and Pregnancy Rates Were AttainedFollowing Hormone Treatment in Sows

Postpartum sows were randomly distributed into three different groupscomprised of Controls, Treatment 1, and Treatment 2, with the exceptionof Site 3, which was divided into two groups, Control and Treatment 2.Control sows were detected for estrus following weaning, and bredfollowing the normal standard operating procedures for the farms onwhich they resided. Treatment 1 sows were detected for estrus followingweaning, and received a 50 mcg dose of deslorelin in the morning whenstanding and were bred by AI 4 hours later and again at 24+/−2 hourslater. Treatment 2 sows received a 50 mcg dose of deslorelin in SAIB at96 or 120 hours post-weaning and were bred with a single insemination28+/−2 hours later with no regard to estrus detection.

As shown in Table 3, Table 4, and Table 5 deslorelin treatment resultedin normal litter sizes in sows regardless of estrus detection.

TABLE 3 Litter Size After Deslorelin Treatment in Sows Site 1 NumberAvg. Total Avg. Total in Group Pigs Born Live Pigs Controls 38 12.7411.35 Treatment 1 39 12.10 11.03 Treatment 2 40 12.37 11.24

TABLE 4 Litter Size After Deslorelin Treatment in Sows Site 2 NumberAvg. Total Avg. Total in Group Pigs Born Live Pigs Controls 68 11.2310.57 Treatment 1 72 11.21 10.25 Treatment 2 66 10.88 10.02

TABLE 5 Litter Size After Deslorelin Treatment in Sows Site 3 NumberAvg. Total Avg. Total in Group Pigs Born Live Pigs Controls 58 11.2610.58 Treatment 2 60 11.09 10.27

As shown in Table 6, normal pregnancy rates were obtained followingdeslorelin treatment in sows.

Table 3, Table 4, and Table 5 demonstrate that normal litter sizes wereattained following treatment with a single dose of deslorelin in SAIB inpostpartum sows. Table 3, Table 4, and Table 5 represent data obtainedfrom three different farm sites. Table 6 summarizes the data from Table2, Table 3, Table 4, and Table 5, and demonstrates that normal pregnancyrates were obtained, following deslorelin treatment in sows.Significantly, these results demonstrate that the same number of pigscan be obtained with the least amount of labor.

TABLE 6 Pregnancy Rate After Deslorelin Treatment in Sows Number Number% in Group Pregnant Pregnant Controls 246 172 69.92% Treatment 2 250 17770.80%

It will be understood that modifications thereof may be suggested tothose skilled in the art, and it is intended to cover all suchmodifications as fall within the scope of appended claims.

1-25. (canceled)
 26. A method of synchronizing ovulation and time ofinsemination in a weaned sow, the method comprising the steps ofadministering to the sow a hormone selected from the group consisting ofa gonadotropin releasing hormone (GnRH), or an analog or derivativethereof, without a multiple sequential hormonal intervention forsynchronizing ovulation, wherein the hormone is administered to the sowafter a timed interval post weaning of the piglets and wherein theadministration of the hormone is performed without heat detection; andbreeding the sow at a defined time after administration of the hormonewherein the breeding step is a single artificial insemination step thatresults in pregnancy of the sow.
 27. The method of claim 26 wherein thehormone is a GnRH analog.
 28. The method of claim 26 wherein the hormoneis in a kit, further comprising instructions for use, wherein theinstructions for use describe steps for synchronizing the time ofinsemination in the sow.
 29. The method of claim 27 wherein the GnRHanalog is administered to the sow four to five days post weaning of thesow.
 30. The method of claim 27 wherein the GnRH analog is administeredto the sow four days post weaning of the sow.
 31. The method of claim 26wherein the hormone is in a composition and the composition is aninjectable composition.
 32. The method of claim 27 wherein the GnRHanalog is in a composition and the composition is an injectablecomposition.
 33. The method of claim 29 wherein the GnRH analog is in acomposition and the composition is an injectable composition.
 34. Themethod of claim 30 wherein the GnRH analog is in a composition and thecomposition is an injectable composition.
 35. The method of claim 34wherein the sow is bred about 28 hours after the hormone isadministered.
 36. The method of claim 26 wherein the hormone is in acomposition and the composition is for an intravaginal route ofadministration.
 37. The method of claim 27 wherein the GnRH analog is ina composition and the composition is for an intravaginal route ofadministration.
 38. The method of claim 29 wherein the GnRH analog is ina composition and the composition is for an intravaginal route ofadministration.
 39. The method of claim 37 wherein the composition is alow-viscosity, polymeric composition.
 40. The method of claim 38 whereinthe composition is a low-viscosity, polymeric composition.
 41. Themethod of claim 26 wherein the hormone is administered in a polymericdelivery device.
 42. The method of claim 29 wherein the GnRH analog isadministered to the sow 96 hours after weaning the piglets.
 43. Themethod of claim 38 wherein the GnRH analog is administered to the sowfour days post weaning.
 44. The method of claim 42 wherein the GnRHanalog is administered to the sow four days post weaning.